Most commercial refrigeration systems utilize a halocarbon refrigerant (e.g. "Freon") in compression-expansion cycles which absorb heat (refrigerate) at the region to be cooled. However, the same refrigerant must give off heat because in the course of the cycle, after compression, it becomes heated to a gaseous state from which it must be cooled for efficient operation. it has long been recognized that the heat available in the superheated refrigerant can be utilized in preheating another volume or liquid. Thus there now are in use various types of preheater systems for the commercial establishments, e.g. supermarkets, hotels, restaurants, hospitals, which widely use closed cycle refrigeration systems and must also heat water.
In one preexisting type of preheater, now employed more than any other, water at normally supplied pressure and temperature is passed into a tank in which an inner wall comprises a hollow cylindrical heat exchanger member. The superheated refrigerant is fed through the interior of this member, which has a dimpled heat exchange surface, for thermal transfer to the body of water within the tank. By this heat exchange the heat taken up by the water cools the refrigerant adequately for the use in each cycle. This known system functions only with refrigeration systems which use an expansion valve receiver, thus not being available for about half of the installed refrigeration systems. Moreover, heat exchange with a peripheral wall in this manner is not efficient and the system is not capable of expansion or reduction if heat exchange needs change.
Another type of preheater system does not use a tank but comprises an external coil which includes an outer wall in which refrigerant passes about an interior tube in which water is passed in the opposite direction. This system is of low heat capacity, and limited efficiency, and requires field modifications including installation of a separate pump.
What is sought for preheating, therefore, is a system which will operate with virtually all refrigeration system types and will do so in a passive mode, requiring no system modification or extra power. The unit should not only be efficient but versatile in being expandable or contractible if a different number of compressors are to be used. The system should operate only in response to gravity and pressure flows of the refrigeration unit without regard to changing pressure or temperature conditions in the refrigerant or water supply during startup or long term operation. There should also be provision for protecting against contamination of potable water by the refrigerant and facility for adding refrigerant if needed.